Intervertebral implant

ABSTRACT

An intervertebral implant includes opposing upper and lower endplates that are configured to engage respective vertebral surfaces in an intervertebral space. The implant carries a plurality of bone fixation spikes that extend out from each endplate. The spikes define a plurality of outer surfaces that extend from a base to a tip. The spikes are laterally staggered, and have a height that increases along a longitudinal direction from the front toward the rear of the implant, and a define recess formed in at least one outer surfaces.

BACKGROUND

Historically, complete removal of a disc from between adjacent vertebraeresulted in fusing the adjacent vertebrae together. This “spinal fusion”procedure, which is still in use today, is a widely accepted surgicaltreatment for symptomatic lumbar and cervical degenerative disc disease.More recently, disc arthoplasty may be utilized to insert an artificialintervertebral disc implant into the intervertebral space betweenadjacent vertebrae. Such a disc implant allows limited universalmovement of the adjacent vertebrae with respect to each other. The aimof total disc replacement is to remove pain generation (caused by adegenerated disc), restore anatomy (disc height), and maintain mobilityin the functional spinal unit so that the spine remains in an adaptedsagittal balance. Sagittal balance is defined as the equilibrium of thetrunk with the legs and pelvis to maintain harmonious sagittal curvesand thus the damping effect of the spine. In contrast with fusiontechniques, total disc replacement preserves mobility in the motionsegment.

One such intervertebral implant includes an upper part mounted to anadjacent vertebra, a lower part mounted to another adjacent vertebra,and an insert located between these two parts. An example of such atotal disc replacement intervertebral implant is shown in U.S. Pat. No.6,936,071, titled “Intervertebral Implant”, the contents of which areincorporated herein by reference in their entirety. To provide an anchorto mount the upper and lower parts to the adjacent vertebrae, each partincludes a vertically extending keel. While this and other knownimplants represent improvements in the art of artificial intervertebralimplants, there exists a continuing need for improvements of these typesof implants.

SUMMARY

In accordance with one embodiment, an endplate of an intervertebralimplant includes an outer transverse bone facing surface configured toengage a respective adjacent vertebral surface. The endplate furtherincludes at least one bone fixation spike projecting out from the bonefacing surface. The fixation spike defines at least one outer surfaceextending between a base and a tip. The tip is outwardly spaced from thebone facing surface, and the bone fixation spike defines a recessextending into the outer surface at a location between the tip and thebase.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofan example embodiment of the application, will be better understood whenread in conjunction with the appended drawings. For the purposes ofillustrating the flexible anchoring keel and related instruments of thepresent application, there is shown in the drawings an exampleembodiment. It should be understood, however, that the application isnot limited to the precise arrangements and instrumentalities shown. Inthe drawings:

FIG. 1A is a perspective view of a pair of vertebral bodies separated byan intervertebral space;

FIG. 1B is a perspective view of the vertebral bodies illustrated inFIG. 1, and an intervertebral implant inserted into the intervertebralspace between the two vertebral bodies;

FIG. 2 is a perspective view of an intervertebral implant illustrated inFIG. 1B, constructed in accordance with one embodiment including firstand second endplates and an articulation disposed between the endplates;

FIG. 3 is an exploded sectional end elevation view of the intervertebralimplant illustrated in FIG. 2 taken along line 3-3;

FIG. 4 is a plan view of an inner transverse surface of the firstendplate illustrated in FIG. 2;

FIG. 5A is a perspective view of the inlay of the intervertebral implantillustrated in FIG. 3;

FIG. 5B is a top plan view of the inlay illustrated in FIG. 5A

FIG. 5C is a side elevation view of the inlay illustrated in FIG. 5A;

FIG. 5D is an end elevation view of the inlay illustrated in FIG. 5B;

FIG. 6 is a perspective view of a lower plate of the intervertebralimplant illustrated in FIG. 2;

FIG. 7A is a side elevation view of the intervertebral implantillustrated in FIG. 2;

FIG. 7B is a side elevation view of the intervertebral implant similarto FIG. 7A, but showing flexion/extension rotation;

FIG. 8A is a front elevation view of the intervertebral implantillustrated in FIG. 2;

FIG. 8B is a front elevation view of the intervertebral implant similarto FIG. 8A, but showing lateral bending rotation;

FIG. 9A is a top plan view of the lower plate of the intervertebralimplant illustrated in FIG. 2;

FIG. 9B is a sectional side elevation view of the intervertebral implantillustrated in FIG. 9A, taken along line 9B-9B;

FIG. 9C is a rear end elevation view of the intervertebral implantillustrated in FIG. 9A;

FIG. 9D is an enlarged top plan view of a region 9D of FIG. 9A,illustrating a first or forward spike of the intervertebral implant;

FIG. 9E is an enlarged top plan view of a region 9E of FIG. 9A,illustrating a second or middle spike of the intervertebral implant;

FIG. 9F is an enlarged top plan view of a region 9F of FIG. 9A,illustrating a third or rear spike of the intervertebral implant;

FIG. 10A is a front perspective view of one of the spikes of theendplate illustrated in FIG. 9A constructed in accordance with oneembodiment;

FIG. 10B is a rear end elevation view of one of the spikes of theendplate illustrated in FIG. 9A constructed in accordance with anotherembodiment;

FIG. 10C is a front elevation view of the spike illustrated in FIG. 10A;

FIG. 10D is a top plan view of one of the spikes of the endplateillustrated in FIG. 9A constructed in accordance with anotherembodiment;

FIG. 10E is a side elevation view of a spike of the endplate illustratedin FIG. 9A constructed in accordance with another embodiment;

FIG. 11A is a top plan view of the upper plate of the intervertebralimplant illustrated in FIG. 2;

FIG. 11B is a sectional side elevation view of the intervertebralimplant illustrated in FIG. 11A, taken along line 11B-11B;

FIG. 11C is a rear end elevation view of the intervertebral implantillustrated in FIG. 11A;

FIG. 11D is an enlarged view of a first or forward spike of theintervertebral implant illustrated in FIG. 11A;

FIG. 11E is an enlarged view of a second or middle spike of theintervertebral implant illustrated in FIG. 11A;

FIG. 11F is an enlarged view of a third or rear spike of theintervertebral implant illustrated in FIG. 11A; and

FIG. 12A is a front perspective view of one of the spikes of theendplate illustrated in FIG. 11A constructed in accordance with oneembodiment;

FIG. 12B is a rear end elevation view of one of the spikes of theendplate illustrated in FIG. 1A constructed in accordance with anotherembodiment;

FIG. 12C is a front elevation view of the spike illustrated in FIG. 12A;

FIG. 12D is a top plan view of one of the spikes of the endplateillustrated in FIG. 11A constructed in accordance with anotherembodiment;

FIG. 12E is a side elevation view of a spike of the endplate illustratedin FIG. 11A constructed in accordance with another embodiment;

FIG. 13A is a perspective view of an endplate carrying a plurality ofbone fixation spikes arranged in accordance with an alternativeembodiment;

FIG. 13B is a perspective view of a bone fixation spike constructed inaccordance with an alternative embodiment;

FIG. 13C is a top plan view of the bone fixation spike illustrated inFIG. 13B;

FIG. 13D is a perspective view of a bone fixation spike constructed inaccordance with an alternative embodiment;

FIG. 13E is a perspective view of a bone fixation spike constructed inaccordance with an alternative embodiment;

FIG. 13F is a side elevation view of the bone fixation spike illustratedin FIG. 13E;

FIG. 13G is a perspective view of a bone fixation spike constructed inaccordance with an alternative embodiment;

FIG. 13H is a perspective view of a bone fixation spike constructed inaccordance with an alternative embodiment;

FIG. 13I is a perspective view of the bone fixation spike illustrated inFIG. 13H;

FIG. 13J is a perspective view of a bone fixation spike constructed inaccordance with an alternative embodiment;

FIG. 13K is a perspective view of a bone fixation spike constructed inaccordance with an alternative embodiment;

FIG. 13L is a perspective view of a bone fixation spike constructed inaccordance with an alternative embodiment;

FIG. 13M is a top plan view of the bone fixation spike illustrated inFIG. 13L; and

FIG. 14 is a side elevation view illustrating the insertion of theintervertebral implant illustrated in FIG. 2 into an intervertebralspace.

DETAILED DESCRIPTION

Referring to FIGS. 1A-B, a superior vertebral body 12 a defines asuperior vertebral surface 13 a of an intervertebral space 14, and anadjacent inferior vertebral body 12 b defines an inferior vertebralsurface 13 b of the intervertebral space 14. Thus, the intervertebralspace 14 is disposed between the vertebral bodies 12 a-b. The vertebralbodies 12 a-b can be anatomically adjacent vertebral bodies, or canremain after a discectomy has been performed that removed a vertebralbody from a location between the vertebral bodies 12 a-b. Asillustrated, the intervertebral space 14 is illustrated after adiscectomy, whereby the disc material has been removed to prepare theintervertebral space 14 to receive an orthopedic implant, such as theintervertebral implant 10 illustrated in FIG. 2. Thus, the implant 10 isconfigured to be inserted into the intervertebral space 14, and achieverestoration of height while maintaining mobility. The intervertebralspace 14 can be disposed anywhere along the spine as desired.

Certain terminology is used in the following description for convenienceonly and is not limiting. The words “right”, “left”, “lower” and “upper”designate directions in the drawings to which reference is made. Thewords “inner” or “distal” and “outer” or “proximal” refer to directionstoward and away from, respectively, the geometric center of the implantand related parts thereof. The words, “anterior”, “posterior”,“superior,” “inferior,” “medial,” “lateral,” and related words and/orphrases designate preferred positions and orientations in the human bodyto which reference is made and are not meant to be limiting. Theterminology includes the above-listed words, derivatives thereof andwords of similar import.

The implant 10 and various components of the implant are describedherein extending horizontally along a longitudinal direction “L” andlateral direction “A”, and vertically along a transverse direction “T”.Unless otherwise specified herein, the terms “lateral,” “longitudinal,”and “transverse” are used to describe the orthogonal directionalcomponents of various components. It should be appreciated that whilethe longitudinal and lateral directions are illustrated as extendingalong a horizontal plane, and that the transverse direction isillustrated as extending along a vertical plane, the planes thatencompass the various directions may differ during use. For instance,when the implant 10 is implanted into an intervertebral space, such asthe intervertebral space 14, the transverse direction T extendsgenerally along the superior-inferior (or caudal-cranial) direction,while the plane defined by the longitudinal direction L and lateraldirection A lie generally in the anatomical plane defined by theanterior-posterior direction, and the medial-lateral direction.Accordingly, the directional terms “vertical” and “horizontal” are usedto describe the implant 10 and its components as illustrated merely forthe purposes of clarity and illustration.

Referring now to FIGS. 1-3 generally, the implant 10 generally includesa first or upper component, such as a first or upper endplate 20 adaptedto engage the superior vertebral body 12 a, and a second or lowercomponent, such as a second or lower endplate 22 adapted to engage theinferior vertebral body 12 b. The endplates 20 and 22, and componentsthereof, can be formed from a variety of biocompatible materials, suchas cobalt chromium molybdenum (CoCrMo), titanium and titanium alloys,stainless steel, ceramics, or polymers such as polyetheretherketone(PEEK), polyetherketoneketone (PEKK), bioresorbable materials, andbonegraft (for example allograft and xenograft). A coating may be addedor applied to the endplates 20 and 22 to improve physical or chemicalproperties. The coatings may help to ensure bony in or on growth ormedication. Examples of coatings include plasma-sprayed titanium coatingor Hydroxyapatite.

The upper endplate 20 includes an upper endplate body 21 that defines alongitudinally front end 23, which provides a leading end with respectto insertion of the implant 10 into the intervertebral disc space 14.The upper endplate body 21 further defines an opposing longitudinallyrear end 25, which provides a trailing end with respect to insertion ofthe implant 10 into the intervertebral disc space 14. The upper endplatebody 21 further defines opposing first and second lateral sides 27 and29, respectively, connected between the front and rear ends 23 and 25,respectively. The upper endplate 20 extends along a central longitudinalaxis L-L that divides the body 21 into first and second opposing lateralregions 49A and 49B, respectively (see FIG. 9A). The lateral side 27defines the lateral boundary of the lateral region 49A, while thelateral side 29 defines the lateral boundary of the lateral region 49B.The upper endplate body 21 further presents an upper, or outertransverse bone facing surface 24, and an opposing lower, or innertransverse surface 43. The upper endplate 20 includes a plurality ofbone fixation spikes 39 projecting transversely outward, or up, from thebone facing surface 24 of the upper endplate body 21.

Similarly, the lower endplate 22 includes a lower endplate body 37 thatdefines a longitudinal front end 47, which provides a leading end withrespect to insertion of the implant 10 into the intervertebral discspace 14. The lower endplate body 37 further defines an opposinglongitudinal rear end 31, which defines a trailing end with respect toinsertion of the implant 10 into the intervertebral disc space 14. Thelower endplate body 37 also defines first and second laterally opposedsides 33 and 35, respectively, connected between the front and rear ends47 and 31, respectively. The lower endplate 22 extends along a centrallongitudinal axis L-L that divides the body 23 into first and secondopposing lateral regions 51A and 51B, respectively (see FIG. 11A). Thelateral side 33 defines the lateral boundary of the lateral region 51A,while the lateral side 35 defines the lateral boundary of the lateralregion 51B. The lower endplate body 37 further presents a lower, orouter transverse bone facing surface 26, and an opposing upper, or innertransverse surface 45. The lower endplate 22 includes a plurality ofbone fixation spikes 41 projecting transversely outward, or down, fromthe bone facing surface 26.

The front and rear ends of the endplates 20 and 22 are separated alongthe longitudinal direction L by a central lateral axis A-A (see FIGS. 9Aand 11A). The bone facing surfaces 24 and 26 are separated along atransverse axis T-T that extends in the transverse direction T. Inaccordance with one embodiment, the front ends 23 and 47 of theendplates 20 and 22 define a posterior end 11 of the implant 10 withrespect to the intervertebral space 14, while the rear ends 25 and 31 ofthe endplates 20 and 22 define an opposing anterior end 13 of theimplant 10 with respect to the intervertebral space 14. Otherwisestated, the front or leading ends 23 and 47 of the endplates 20 and 22are inserted into the posterior region of the intervertebral space 14,while the rear or trailing ends 25 and 31 of the endplates 20 and 22 areinserted into the anterior region of the intervertebral space 14. Theimplant 10 is configured to be inserted into the intervertebral space 14along a forward longitudinal direction that extends from the rear end 13toward the front end 11.

Referring now to FIGS. 3-6, the endplates 20 and 22 each carrycomplementary first and second joint members 75 and 77, respectively,which each provide rounded mating surfaces and are in operative contactwith each other so as to provide an articulating joint 42 that allowsthe endplates 20 and 22 universal movement relative to each other. Thefirst joint member 75 can be provided as a plastic insert 44 supportedby the upper endplate 20, while the second joint member 77 can beprovided as a plastic inlay 48 supported by the lower endplate 22. Theinsert 44 defines a first joint surface 46 or articulation surface, andthe plastic inlay 48 defines a second joint surface 50 or articulationsurface that interfaces with the first joint surface 46, such that thejoint 42 is configured to pivot the endplates 20 and 22 relative to eachother universally about 360°. The joint 48 can be constructed generallyas described in U.S. Pat. No. 7,204,852, the disclosure of which ishereby incorporated by reference as if set forth in its entirety herein,or in accordance with any suitable alternative embodiment. The jointmembers 75 and 77 can be made of any suitable material as desired, suchas cobalt chromium, and the joint surface 50 can be made of any suitablematerial as desired, such as polyethylene. The endplates 20 and 22 canbe made from any suitable material as desired, such aspolyetheretherketone (PEEK), metal, or the like.

As illustrated in FIGS. 3-4, the upper endplate 20 includes a generallycircular pocket 52 that extends into the lower surface 43 of the upperendplate body 21. The pocket 52 has a depth that is less than the heightof the upper endplate body 21, such that the pocket 52 terminates at abase 53 without extending through the endplate body 21. The pocket 52has an outer perimeter 57 that is inwardly recessed with respect to thefront end 23, the rear end 25, and the lateral sides 27 and 29. Theperimeter 57 can be in the shape of a circle, square, rectangle, or anyalternative shape as desired. The pocket 52 can further be stepped so asto define a peripheral shoulder 55 that is upwardly spaced with respectto the lower surface 43, and downwardly spaced with respect to the base53 of the pocket 52.

The insert 44 includes an insert body 54 that defines a first or upperend 56, an opposing second or lower end 58, and at least one side 60extending between the upper and lower ends 56 and 58 that corresponds inshape with the perimeter 57 of the pocket 52. The insert 44 includes alip 62 that projects out from the lower end 58 of the side 60. The lip62 is recessed from the upper end 56 a distance substantially equal tothe distance that the shoulder 55 of the pocket 52 is spaced withrespect to the lower surface 43.

Accordingly, the insert body 54 is configured to nest within the pocket52, such that the lip 62 of the insert body 54 is seated against theshoulder 55 of the pocket, and the upper end 56 is seated against thebase 53. The insert 44 can be connected to the upper endplate 20integrally or discretely, for instance using any suitable attachmentmechanism, such as an adhesive, or complementary engagement features,e.g., threads, that mate so as to lock the insert body 54 in the pocket52. The lip 62 has a height greater than that of the shoulder 55 of thepocket 52, such that the lip 62 projects transversely inward, or down,from the lower surface 43 once the insert 44 has been fastened in thepocket 52 of the upper endplate 20.

The insert 44 defines a concavity 64 that projects upwards into thelower end 58 of the insert body 54. The concavity 64 defines the firstjoint surface 46, which is round as illustrated. The first joint surface46 defines a middle portion 46 a that is recessed with respect to thelower surface 43 of the upper endplate body 21, and an outer portion 46b that projects down from the lower surface 43 of the upper endplatebody 21. In accordance with one embodiment, the first joint surface 46is substantially dome shaped, thereby permitting 360° articulationbetween the upper and lower plates 20 and 22, respectively.Alternatively, the first joint surface 46 can be rounded in one or moredirections, for instance the longitudinal direction L and/or the lateraldirection A if selective articulation is desired. Alternatively still,the first joint surface 46 can be non-rounded if it is desired toprevent the upper and lower plates 20 and 22 from articulating. In thisregard, it should be appreciated that the upper and lower plates 20 and22 can articulate with relative to each other, can be fixed with respectto each other, and can be discretely or integrally connected.

Referring now also to FIGS. 5A-D, the inlay 48 includes an inlay body 68that defines a base 70 having a front end 72, a longitudinally opposingrear end 74, and laterally opposing sides 76 extending between the frontand rear ends 72 and 74. The inlay 48 further includes a substantiallydome-shaped projection 79 laterally centered on the base 70, andlongitudinally displaced closer to the front end 72 than the rear end74. The projection 79 defines the second joint surface 50, which isround and substantially dome-shaped, as illustrated. The dome-shapedsecond joint surface 50 is defined by a radius substantially equal tothat of the dome-shaped first joint surface 46 of the concavity 64, suchthat the first and second joint surfaces 46 and 50, when engaged, canride along each other as the first and second endplates 20 and 22articulate or pivot relative to each other. The projection 79 has aheight greater than the depth of the concavity 64, such that the base 70is spaced from the lower surface 43 of the upper endplate 20 when thejoint surfaces 46 and 50 are engaged. While the second joint surface 50is dome-shaped as illustrated, it should be appreciated that the secondjoint surface 50 can assume any shape as desired as described above withrespect to the first joint surface 46, such that the shape of the firstand second joint surfaces 46 and 50 are complementary.

The inlay body 68 further includes a pair of guide wings 78 that projectlaterally out from the sides 76, and a snap-in projection 80 in the formof a wedge 82 that projects down from the base 70. The wedge 82 presentsa beveled outer surface 84 that extends upward along a longitudinallyforward direction, and a transverse stop surface 86 disposed rearwardwith respect to the beveled outer surface 84. The guide wings 78 andsnap-in projection 80 facilitate insertion of the inlay 48 into thelower endplate 22, as will now be described.

In particular, referring also to FIG. 6, the lower endplate 22 includesan outer rim 50 that extends inward from the upper ends of the opposinglateral sides 33 and 35 and the front end 47 of the lower endplate body37. The lower endplate body 37 thus defines a channel 88 between theupper transverse surface 45, the outer rim 50, and the lateral sides 33and 35 and front end 47 (see also FIG. 11B). The lower endplate 22further includes an inwardly projecting snap-in recess 90 disposedproximate to the rear end 31 of the endplate body 37. The recess 90defines a beveled surface 92 that is angled transversely upward along alongitudinally forward direction. The recess 90 further defines atransverse stop surface 94 disposed rearward of the beveled surface 92.During assembly of the implant 10, the guide wings 78 are inserted intothe channel 88, and the inlay 48 is translated forward along the lowerendplate body 37 until the snap-in projection 80 of the inlay 48 snapinto the snap-in recess 90 of the lower endplate 22, thereby preventinginadvertent removal of the inlay 48. It should be appreciated that theinlay 48 can alternatively be attached to the lower endplate 22, eitherintegrally or discretely in any manner as desired.

Referring now to FIGS. 7A-B, once the insert 44 of the upper endplate 20and the inlay 48 of the lower endplate 22 engage, the upper and lowerendplates 20 and 22 can pivot relative to each other about a lateralaxis, for instance to accommodate flexions and extension of thevertebrae 12 a-b. Similarly as illustrated in FIGS. 8A-B, the upper andlower endplates 20 and 22 can pivot relative to each other about alongitudinal axis, for instance to accommodate lateral bending of thevertebrae 12 a-b. Alternatively, the pivot axis can lie in anyorientation within the horizontal plane defined by the longitudinal andlateral directions. The pivot axis can be coincident with thelongitudinal and lateral directions as illustrated in FIGS. 7A-B andFIGS. 8A-B, or the pivot axis can be offset up to 180° with respect toeither or both of the longitudinal and lateral directions.

While the joint 42 has been described in accordance with one embodiment,it should be appreciated that the implant 10 could include anyalternatively constructed joint (for instance a compliant material suchas a silicon cushion joined between the endplates 20 and 22) thatenables relative motion between the endplates 20 and 22 in anydirection, or that fixedly attaches the endplates 20 and 22. In thisregard, it should be appreciated that the upper endplate 20 could carrythe second joint member 77 or inlay 48, and the lower endplate 22 couldcarry the first joint member 75 or insert 44.

The implant 10 can define a width extending along the lateral directionA that can be between approximately 13-20 mm, a length extending alongthe longitudinal dimension L that can be approximately 10-18 mm, and aheight extending between the outer surfaces 24 and 26 along thetransverse direction T that can be approximately 4-9 mm. Thus, theimplant 10 is suitable for implantation in an intervertebral space inthe cervical and upper thoracic regions of the spine, which ischaracterized by the need for precision because of the relatively smalldimensions of cervical intervertebral spaces.

The dimensions described above with respect to the implant 10 in theillustrated embodiment are in contrast to the dimensions of the implant10 if the implant were to be inserted into an intervertebral space inthe a different spinal region, for instance the lumbar or thoracicregion. For instance, when the implant 10 is configured for implantationinto the lumbar region, the implant can have a width of approximately25-37 mm, a length of approximately 30-56 mm, and a height ofapproximately 8-14 mm.

It is to be understood that the implant 10 can be constructed with anydimensions desirable for implantation of any intervertebral space alongthe spine, and is not limited to the cervical and lumbar regions unlessotherwise indicated. Furthermore, while the implant 10 is configured asa total disc replacement device, implants constructed in accordance withthe teachings described herein are readily configurable for use with arange of bone-anchored orthopedic prostheses, such as interbody spacers,hip and knee replacement implants, and the like. Furthermore, while theimplant 10 has been generally described in accordance with oneembodiment, it should be appreciated that the implant 10 canalternatively be constructed in accordance with any embodiment, suchthat the implant defines an upper, or superior, bone facing surface andan opposing lower, or inferior, bone facing surface. In one alternativeembodiment, either or both of the endplates 20 and 22 can include a keelas described in U.S. Pat. No. 7,204,852, the disclosure of which ishereby incorporated by reference as if set forth in its entirety herein.

Referring now to FIGS. 9A-F and 10A-E, the bone facing surface 24 of theupper endplate body 21 includes a longitudinally front section 24 a, alongitudinally rear section 24 c, and an intermediate section 24 bextending longitudinally between the front section 24 a and the rearsection 24 c. Each section 24 a-c extends laterally between the firstand second lateral sides 27 and 29, which can both be beveled asillustrated. The upper endplate 20 includes laterally opposing notches85 extending into the rear end 25 of the endplate body 21 that are sizedand shaped to receive the distal end of an upper arm of insertion toolconfigured to insert the implant into an intervertebral space.

The front section 24 a extends down, or transversely inward, withrespect to a longitudinally forward direction along the bone facingsurface 24, and terminates at the front end 23 of the endplate body 21.The rearward section 24 c extends down, or transversely inward, withrespect to a longitudinally rearward direction along the bone facingsurface 24, and terminates at the rear end 25 of the endplate body 21.The front section 24 a is longitudinally longer than the rear section 24c, and extends further down than the rear section 24 c. The intermediatesection 24 b extends substantially horizontally between the frontsection 24 a and the rear section 24 c. It should be appreciated thatthe bone facing surface 24 has been described in accordance with theillustrated embodiment, and the surface 24 could assume any alternativeshape as desired. For instance, the surface 24 can be substantiallyplanar, or can include at least one non-planar surface, such as thethree surfaces 24 a-c illustrated and described above.

As described above, the upper endplate 20 includes at least one spike39, such as a plurality of spikes 39 projecting up from the bone facingsurface 24 of the endplate body 21. The spikes 39 are arranged in firstand second symmetrical and substantially identically constructed groups100A and 100B. The first group 100A of spikes 39 is disposed in thelateral region 49A of the endplate body 21, and the second group 100B isdisposed in the lateral region 49B of the endplate body 21. Each group100A-B includes a first or longitudinally forward or front spike 39A, asecond or longitudinally middle spike 39B, and a third or longitudinallyrear spike 39C, such that the longitudinally middle spike 39B isdisposed longitudinally between the forward spike 39A and the rear spike39C, and forward of the central lateral axis A-A. The spikes 39A-C ofthe first group 100A can be constructed substantially identically andsymmetrically with respect to the spikes 39A-C of the second group 100B.

Each spike 39 can include as many surfaces 102 as desired, such as atleast one surface 102, and has substantially pyramidal shape inaccordance with the illustrated embodiment. Each spike 39 extends upfrom a base 104 having a triangular or alternatively shaped footprint atthe bone facing surface 24, to an upper or outer transverse tip 106.Each surface 102 extends between the base 104 and the tip 106, and canbe connected between the base 104 and the tip 106 as illustrated. Thespike 39 thus defines a transverse axis 115 that extends transverselybetween the outer tip 106 and the bone facing surface 24.

The tips 106 of each spike 39A-C of each group 100A-B can be laterallyoffset from each other. Accordingly, the spikes 39 can each create theirown tracks in the complementary vertebral surface 13 a during insertionof the implant 10, and thus engage the bone so as to resist expulsionforces. In accordance with the illustrated embodiment, the tip 106 ofthe forward spike 39A is disposed laterally inward with respect to thetips 106 of the both the middle spike 39B and the rear spike 39C. Thetip 106 of the middle spike 39B is disposed laterally outward withrespect to the tips 106 of the both the forward spike 39A and the rearspike 39C. The tip 106 of the rear spike 39C is disposed laterallyoutward with respect to the tip 106 of the forward spike 39A, andlaterally inward with respect to the tip 106 of the middle spike 39B. Asillustrated, the tips 106 of the middle spike 39B and the rear spike 39Ccan be longitudinally spaced from each other a distance greater than thelongitudinal distance that the tip 106 of the forward spike 39A and thetip 106 of the middle spike 39B are spaced. For instance, in accordancewith one embodiment, the bases 104 of each of the longitudinally spacedspikes 39A-C are longitudinally spaced from each other.

The tip 106 is disposed at a location that is laterally andlongitudinally inside the triangular footprint of the base 104.Alternatively, the tip 106 can be disposed on the boundary of thefootprint of the base 104, or outside the footprint of the base 104 ifdesired. Each spike 39 can include three surfaces 102 a-c that eachextend along an outer transverse directional component, and thus extendout, or up, from the base 104 toward the tip 106. The surfaces 102 a-ccan be substantially triangular in shape as illustrated, or canalternatively assume any suitable geometric shape as desired. Thesurfaces 102 a-c can extend up from the base 104, and terminate at thetip 106.

Each spike 39 includes a pair of front surfaces 102 a and 102 b thateach extends along a direction having an outer transverse directionalcomponent (e.g., extending up from the bone facing surface 24), alongitudinally rearward directional component (e.g., angledlongitudinally rearward along an outer transverse direction along thesurfaces 102 a-b), and a laterally inward directional component (e.g.,angled laterally inward along an outer transverse direction along thesurfaces 102 a-b). Otherwise stated, a line extending up from the base104 along the surfaces 102 a-b will travel longitudinally rearward andlaterally inward. In accordance with alternative embodiments, it shouldbe appreciated that the front surfaces 102 a-b can extend along adirection that has at least one of the above-mentioned directionalcomponents. For instance, it should be appreciated that the surfaces 102a-b could alternatively extend perpendicular with respect to the bonefacing surface 24. Each of the surfaces 102 a-c extends at an angle withrespect to a horizontal plane, defined by the lateral and longitudinaldirections, within a range having a lower end greater than 0°, and anupper end less than or equal to 90°.

In accordance with the illustrated embodiment, the front surface 102 aof each spike 39 is disposed laterally inward with respect to the frontsurface 102 b. Otherwise stated, the front surface 102 a defines amedial surface of the spike 39, while the front surface 102 b defines alateral surface of the spike 39. The front surfaces 102 a-b convergelaterally along the outer transverse direction from the base 104 to thetip 106. The front surfaces 102 a-b further laterally converge along aforward longitudinal direction to a front tip 108. The front surfaces102 a and 102 b extend from the base 104 to the outer transverse tip106, and are joined to each other at their upper ends at a frontinterface 105. The front interface 105 extends in a substantiallylongitudinal direction between the front tip 108 and the outertransverse tip 106. The front surfaces 102 a-b thus diverge from thefront tip 108 along the longitudinally rearward direction, and terminateat a rear surface 102 c. It should be appreciated that the spikes 39 aredescribed with respect to their orientation as illustrated, and that thespikes 39 could be alternatively oriented such that the surfaces 102 a-cextend in any direction as desired.

The rear surface 102 c extends along a direction that has an outertransverse directional component, and a longitudinally forwarddirectional component. Otherwise stated, the rear surface 102 c extendstransversely out from the bone facing surface 24, and a line extendingalong the rear surface 102 c in the transversely outward directionextends longitudinally forward. In accordance with the illustratedembodiment, the rear surface 102 c extends longitudinally forward fromthe base 104 and terminates at the tip 106. In accordance withalternative embodiments, it should be appreciated that the rear surface102 c can extend along a direction that has at least one of theabove-mentioned directional components. For instance, it should beappreciated that the surfaces 102 a-b could alternatively extendperpendicular with respect to the bone facing surface 24.

As illustrated, the rear surface 102 c extends laterally between therear ends of the forward surfaces 102 a-b, so as to define a first rearinterface 107 with respect to the front surface 102 a, and a second rearinterface 109 with respect to the front surface 102 b. The rearinterfaces 107 and 109 each extend longitudinally forward from,transversely out from, and laterally in from, the base 104 in adirection toward the tip 106. The interfaces 105, 107, and 109 canextend substantially straight, or can assume any alternative shape, suchas curved, as desired. As illustrated in FIG. 10D, the spikes define adistance D extending linearly from the front tip 108 to the innertransverse ends of the rear interfaces 107 and 109 within a rangebetween approximately 1.5 mm and 2.0 mm.

As illustrated in FIG. 9B, the interface 105 defines a first angle θ₁with respect to the longitudinal axis L-L, and the interfaces 107 and109 define a second angle θ₂ with respect to the longitudinal axis L-Lthat is bigger than the first angle θ₁. Alternatively, it should beappreciated that the second angle θ₂ can be less than or equal to thefirst angle θ₁. The angles can further be different for each spike. Asillustrated in FIG. 10E, in accordance with one embodiment, theinterface 105 defines an angle α₁ between about 0° and about 15° withrespect to a transverse axis, and the interface 105 defines an angle α₂between about 30° and about 60° with respect to the interface 107.

The interfaces 105 and 107, in combination with the base 104, define anacute triangle with respect to a view from the longitudinal axis L-Ltoward the corresponding lateral side, and further respect to a viewfrom the corresponding lateral side toward the longitudinal axis L-L.Alternatively, the interfaces 105 and 107 and the base 104 could definean isosceles triangle, an equilateral triangle, a right triangle, anobtuse triangle, or any alternative geometric shape as desired.Likewise, the interfaces 105 and 109, in combination with the base 104,define an acute triangle with respect to a view from the longitudinalaxis L-L toward the corresponding lateral side, and further respect to aview from the corresponding lateral side toward the longitudinal axisL-L. Alternatively, the interfaces 105 and 109 and the base 104 coulddefine an isosceles triangle, an equilateral triangle, a right triangle,an obtuse triangle, or any alternative geometric shape as desired. Asillustrated in FIG. 9D-F, the interfaces 107 and 109, in combinationwith the base 104, define an isosceles triangle, though it should beappreciated that the interfaces 107, 109, and the base 104 couldalternatively define an equilateral triangle, a right triangle, anobtuse triangle, or any alternative geometric shape as desired.

Referring now to FIGS. 9A-C, each of the spikes 39A-C defines anabsolute height H_(A) with respect to the bone facing surface 24, and arelative height H_(R), when the endplate is horizontally oriented, withrespect to a common horizontal plane H extending along the lateral andlongitudinal directions, such as the inner transverse surface 43, or theinner transverse surface 45 of the lower endplate 22 when the implant isin a horizontally oriented, non-articulated, position. In accordancewith the illustrated embodiment, the absolute height H_(A) can bebetween 0.5 mm and 4.0 mm, including a range between approximately 1.5mm and approximately 2.5 mm, such as a range between approximately 1.5mm and approximately 2.0 mm (see also FIG. 10B). The relative heightH_(R) can be between approximately 1.5 mm and approximately 10 mm,including a range between approximately 2.0 mm and approximately 7.0 mm.

In accordance with the illustrated embodiment, the relative height H_(R)of at least two of the spikes 39, up to all of the spikes 39, canincrease in a longitudinally rearward direction. Otherwise stated, thetransverse distance between a common horizontal plane from therespective outer transverse tip 106 of each spike 39 increases along thelongitudinally rearward direction. Accordingly, the relative height ofthe forward spike 39A is less than the relative height of the relativeheight of the middle spike 39B, which in turn is less than the relativeheight of the rear spike 39C. The difference in relative height betweenthe forward spike 39A and the middle spike 39B is greater than thedifference in relative height between the middle spike 39B and the rearspike 39C in accordance with the illustrated embodiment.

However, because the bone facing surface 24 is non-planar in accordancewith the illustrated embodiment, the relationship of the absoluteheights of the spikes 39A-C with respect to each other need not be asdescribed with respect to the relative heights of the spikes 39A-C. Forinstance, because the base 104 of the forward spike 39A is disposedbelow the base 104 of the middle spike 39B, the absolute height of theforward spike 39A can be greater than the absolute height of the middlespike 39B, such that the relative height of the forward spike 39A isless than the relative height of the middle spike 39B. However, becausethe base 104 of the rear spike 39C is disposed below the base 104 of themiddle spike 39B, the rear spike 39C has an absolute height that isgreater than the absolute height of the middle spike 39B, such that therear spike 39C has a relative height greater than that of the middlespike 39B as described above.

It should be appreciated that the relationship of the absolute heightsof the spikes 39A-C with respect to each other can therefore depend onthe shape of the bone facing surface 24. For instance, if the bonefacing surface 24 is substantially planar, then the absolute height ofthe forward spike 39A would be less than that of the middle spike 39B,which would be less than that of the rear spike 39C.

With continuing reference to FIGS. 9A-F, at least one up to all of thespikes 39A-C defines a recess 110 extending into at least one of thesurfaces 102 a-c. For instance, the forward spike 39A defines a recess110 extending into the laterally outer front surface 102 a, while themiddle spike 39B and the rear spike 39C each defines a recess 110extending into the laterally inner front surface 102 b and the rearsurface 102 c. FIG. 10B illustrates a recess 110 extending into the rearsurface 102 c of a spike 39. FIGS. 10A and 10C illustrate a recessextending into the front surfaces 102 a and 102 b. FIG. 10D illustratesa recess 110 extending into all surfaces 102 a-c. The recess 110extending into the laterally front surface 102 a extends between thefront interface 105 and the rear interface 107. Similarly, the recess110 extending into the laterally inner front surface 102 b extendsbetween the front interface 105 and the rear interface 109. The recess110 extending into the rear surface 102 c extends between the rearinterfaces 107 and 109.

Thus, in accordance with one embodiment, the recess 110 extends into therespective surface 102 along at least one or both of a lateraldirectional component and a longitudinal directional component.Furthermore, in accordance with one embodiment, the recess 110 projectsinward with respect to a plane defined by at least two outer edges ofthe surface 102 in which the recess 110 is disposed. Alternatively, theentire surface 102 can be provided in the shape of the recess 110.

Because at least one of the spikes 39 defines a recess 110 in its medialside, and at least one of the spikes 39 defines a recess 110 in itslateral side, movement of the implant 10 is restricted as the spikes 39penetrate the complementary vertebral surface 13 a. It should beappreciated, however, that the spikes 39A-C can alternatively define arecess in one or more, up to all, of the surfaces 102 a-c. For instance,the spikes 39 can define a first recess 110 in one of the surfaces 102,and a second recess in another one of the surfaces 102. Alternatively oradditionally, a single recess 110 can extend into a pair of adjacentsurfaces 102.

The recess 110 is vertically or transversely elongate, and extends upfrom the base 104 and terminates at a location transversely inward ofthe tip 106. In accordance with the illustrated embodiment, the recess110 is shaped as arc in the horizontal plane, that is transverselyelongate so as to define a partial cylindrical surface, and is providedin one embodiment as a cut out of the corresponding surface or surfaces102 a-c. For instance, a cylindrical bore 112 can be milled or otherwiseformed into, but not through, the endplate 20. The location of the bore112 can be disposed adjacent a desired surface of the spike 39, suchthat the milling operation cuts the cylindrically shaped recess 110 intothe spike 39. It should be appreciated that the milling operation neednot extend into the endplate 20, but could instead terminate once therecess 110 has reached its desired transverse depth, for instance to thebase 104 of the spike 39. The depth of the recess 110 into the surface102 of the spike 39 can thus depend on the alignment between thelocation of the bore 112 and the surface 102.

As illustrated in FIG. 9B, the recess 110 extending into the inner frontsurface 102 of the middle spike 39B has a height bigger than the recess110 extending into the inner front surface 102 of the rear spike 39C,though the height of the recess 110 of the middle spike 39B could beequal to or less than that of the rear spike 39C. Likewise, the heightof the recess 110 of the forward spike 39A could be equal to, greaterthan, or less than, that of the middle spike 39B and rear spike 39C. Asillustrated in FIGS. 9D-F, the recesses 110 are arc-shaped in transversecross section, and extend less than 180° as illustrated, though the arccan alternatively have any length as desired. In accordance with theillustrated embodiment, the arc length of the recesses 110 increasesalong an inner transverse direction. Of course, it should be appreciatedthat the arc length of the recesses 110 could alternatively remainsubstantially constant along an inner transverse direction. Furthermore,it should be appreciated that the recesses 110 can be provided as anyshape projecting into the respective surface or surfaces 102 of thespike, for instance a polygonal shape such as triangular, rectangular,hexagonal, octagonal, or an oval or any other shape as desired. It hasbeen found that the recesses 110 reduce the cross-sectional dimension ofthe spikes 39, and thus are easily penetrable into the complementaryvertebral surface 13 a.

It should be appreciated that while the spikes 39 have been described inaccordance with the illustrated embodiment, the spikes 39 can have anysuitable alternative shape as desired. For instance, one or more, up toall of the surfaces 102 a-c could be shaped in accordance with anysuitable alternative embodiment. It should further be appreciated thatthe spikes 39 are not intended to be limited to having the threesurfaces 102 a-c. Rather, in accordance with one embodiment, at leastone of the spikes 39 has at least one surface that defines a recess,such as the recess 110 as illustrated and described above.

It should be appreciated that while each group 100A-B includes threespikes 39 as illustrated, each group can include any number of spikes39, including less than three and more than three, for instance at leastone spike 39. In general, higher loads experienced by the implant 10 canjustify a greater number of spikes. For instance, each group can includeten or more spikes when the implant 10 is implemented in the lumbarregion. The at least one spike 39 can be disposed in any of the frontsection 24 a, the intermediate section 24 b, and the rear section 24 c.

Furthermore it should be appreciated that the upper endplate 20 includesat least one spike 39 that can be disposed at either the first lateralregion 49A, the second lateral region 49B, or coincident with thecentral longitudinal axis L-L. Furthermore, it should be appreciatedthat each of the spikes 39 can be constructed in accordance with any ofthe embodiments as described above with respect to spikes 39A-C. Itshould also be appreciated that the spikes 39A-C of the first group 100Acan be constructed substantially identically with respect to thecorresponding spikes 39A-C of the second group 100B as illustrated, oralternatively the spikes 39A-C of the first group 100A can beconstructed differently than the corresponding spikes 39A-C of thesecond group 100B.

Referring now to FIGS. 11A-F, the bone facing surface 26 of the lowerendplate body 37 is beveled at its front end 47, and includes asubstantially planar horizontal surface 26 a that extends generallyparallel with the inner surface 45. The horizontal surface 26 a extendslaterally between the first and second lateral sides 33 and 35, whichcan both be beveled as illustrated. The lower endplate 22 includeslaterally opposing notches 87 extending into the rear end 31 of theendplate body 37 that are sized and shaped to receive the distal end ofa lower arm of insertion tool configured to insert the implant 10 intoan intervertebral space. It should be appreciated that the bone facingsurface 26 has been described in accordance with the illustratedembodiment, and the surface 26 could assume any alternative shape asdesired. For instance, the surface 26 can be constructed substantiallyas described with respect to the bone facing surface 24 of the upperendplate 20, or in accordance with any desired alternative embodiment.

As described above, the lower endplate 22 includes at least one spike41, such as a plurality of spikes 41 projecting down from the bonefacing surface 26 of the endplate body 37. In accordance with theillustrated embodiment, the spikes 41 project down from the planarsurface 26 a. The spikes 41 are arranged in first and second symmetricaland substantially identically constructed groups 120A and 120B. Thefirst group 120A of spikes 41 is disposed in the lateral region 51A ofthe endplate body 37, and the second group 120B is disposed in thelateral region 51B of the endplate body 37. Each group 120A-B includes alongitudinally forward or front spike 41A, a longitudinally rear spike41C, and a longitudinally middle spike 41B disposed longitudinallybetween the forward spike 41A and the rear spike 41C, and forward of thecentral lateral axis A-A. The spikes 41A-C of the first group 120A canbe constructed substantially identically and symmetrically with respectto the spikes 41A-C of the second group 120B.

Each spike 41 can include as many surfaces 122 as desired, such as atleast one surface 122, and has substantially pyramidal shape inaccordance with the illustrated embodiment. Each spike 41 extends upfrom a base 124 having a triangular or alternatively shaped footprint atthe bone facing surface 26, to an upper or outer transverse, tip 126.Each surface 122 extends between the base 124 and the tip 126, and canbe connected between the base 124 and the tip 126 as illustrated. Thespike 41 thus defines a transverse axis 135 that extends transverselybetween the outer tip 126 and the bone facing surface 26.

The tips 126 of each spike 41A-C of each group 120A-B can be laterallyoffset from each other. Accordingly, the spikes 41 can each create theirown tracks in the complementary vertebral surface 13 a during insertionof the implant 10, and thus engage the bone so as to resist expulsionforces. In accordance with the illustrated embodiment, the tip 126 ofthe forward spike 41A is disposed laterally inward with respect to thetips 126 of the both the middle spike 41B and the rear spike 41C. Thetip 126 of the middle spike 39B is disposed laterally outward withrespect to the tips 126 of the both the forward spike 41A and the rearspike 41C. The tip 126 of the rear spike 41C is disposed laterallyoutward with respect to the tip 126 of the forward spike 41A, andlaterally inward with respect to the tip 126 of the middle spike 41B. Asillustrated, the tips 126 of the middle spike 419B and the rear spike41C can be longitudinally spaced from each other a distance greater thanthe longitudinal distance that the tip 126 of the forward spike 41A andthe tip 126 of the middle spike 41B are spaced. For instance, inaccordance with one embodiment, the bases 124 of each of thelongitudinally spaced spikes 41A-C are longitudinally spaced from eachother.

The tip 126 is disposed at a location that is laterally andlongitudinally inside the triangular footprint of the base 124.Alternatively, the tip 126 can be disposed on the boundary of thefootprint of the base 124, or outside the footprint of the base 124 ifdesired. Each spike 41 can include any number of surfaces as desired,such as the three surfaces 122 a-c illustrated, that each extend alongan outer transverse directional component, and thus extend out, or down,from the base 124 toward the tip 126. The surfaces 122 a-c can besubstantially triangular in shape as illustrated, or can alternativelyassume any suitable geometric shape as desired. The surfaces 122 a-c canextend down from the base 124, and terminate at the tip 126.

Each spike 41 includes a pair of front surfaces 122 a and 122 b thateach extends along a direction having an outer transverse directionalcomponent (e.g., extending down from the bone facing surface 26), alongitudinally rearward directional component (e.g., angledlongitudinally rearward along an outer transverse direction along thesurfaces 122 a-b), and a laterally inward directional component (e.g.,angled laterally inward along an outer transverse direction along thesurfaces 122 a-b). Otherwise stated, a line extending down from the base124 along the surfaces 122 a-b will travel longitudinally rearward andlaterally inward. In accordance with alternative embodiments, it shouldbe appreciated that the front surfaces 122 a-b can extend along adirection that has at least one of the above-mentioned directionalcomponents. For instance, it should be appreciated that the surfaces 122a-b could alternatively extend perpendicular with respect to the bonefacing surface 26.

In accordance with the illustrated embodiment, the front surface 122 aof each spike 41 is disposed laterally inward from the front surface 122b. Otherwise stated, the front surface 122 a defines a medial surface ofthe spike 41, while the front surface 122 b defines a lateral surface ofthe spike 41. The front surfaces 122 a-b converge laterally along theouter transverse direction from the base 124 to the tip 126. The frontsurfaces 122 a-b further laterally converge along a forward longitudinaldirection to a front tip 128. The front surfaces 122 a and 122 b extendfrom the base 124 to the outer transverse tip 126, and are joined toeach other at their upper ends at a front interface 125. The frontinterface 125 extends in a substantially longitudinal direction betweenthe front tip 128 and the outer transverse tip 126. The front surfaces122 a-b thus diverge from the front tip 128 along the longitudinallyrearward direction, and terminate at a rear surface 122 c. It should beappreciated that the spikes 41 are described with respect to theirorientation as illustrated, and that the spikes 41 could bealternatively oriented such that the surfaces 122 a-c extend in anydirection as desired.

The rear surface 122 c extends along a direction that has an outertransverse directional component, and a longitudinally forwarddirectional component. Otherwise stated, the rear surface 122 c extendstransversely out from the bone facing surface 26, and a line extendingalong the rear surface 122 c in the transversely outward directionextends longitudinally forward. In accordance with the illustratedembodiment, the rear surface 122 c extends longitudinally forward fromthe base 124 and terminates at the tip 126. In accordance withalternative embodiments, it should be appreciated that the rear surface122 c can extend along a direction that has at least one of theabove-mentioned directional components. For instance, it should beappreciated that the surfaces 122 a-b could alternatively extendperpendicular with respect to the bone facing surface 26. Each of thesurfaces 122 a-c extends at an angle, with respect to a horizontal planedefined by the lateral and longitudinal directions, within a rangehaving a lower end greater than 0°, and an upper end less than or equalto 90°.

As illustrated, the rear surface 122 c extends laterally between therear ends of the forward surfaces 122 a-b, so as to define a first rearinterface 127 with respect to the front surface 122 a, and a second rearinterface 129 with respect to the front surface 122 b. The rearinterfaces 127 and 129 each extend longitudinally forward from,transversely out from, and laterally in from, the base 124 in adirection toward the tip 126. The interfaces 125, 127, and 129 canextend substantially straight, or can assume any alternative shape, suchas curved, as desired. As illustrated in FIG. 12D, the spikes define adistance D extending linearly from the front tip 128 to the innertransverse ends of the rear interfaces 127 and 129 within a rangebetween approximately 1.5 mm and 2.0 mm.

Referring also to FIG. 12E, the interface 125 defines a first angle α1with respect to the longitudinal axis L-L, and the interfaces 127 and129 define a second angle α2 with respect to the longitudinal axis L-Lthat is greater than the first angle α1. Alternatively, it should beappreciated that the second angle α2 can be less than or equal to thefirst angle α1. In accordance with one embodiment, as illustrated inFIG. 12E, the interface 127 defines an angle α1 between about 0° andabout 15° with respect to a transverse axis, and the interface 125defines an angle α2 between about 30° and about 60° with respect to theinterface 127.

The interfaces 125 and 127, in combination with the base 124, define anacute triangle with respect to a view from the longitudinal axis L-Ltoward the corresponding lateral side, and further respect to a viewfrom the corresponding lateral side toward the longitudinal axis L-L.Alternatively, the interfaces 125 and 127 and the base 124 could definean isosceles triangle, an equilateral triangle, a right triangle, anobtuse triangle, or any alternative geometric shape as desired.Likewise, the interfaces 125 and 129, in combination with the base 124,define an acute triangle with respect to a view from the longitudinalaxis L-L toward the corresponding lateral side, and further respect to aview from the corresponding lateral side toward the longitudinal axisL-L. Alternatively, the interfaces 125 and 109 and the base 124 coulddefine an isosceles triangle, an equilateral triangle, a right triangle,an obtuse triangle, or any alternative geometric shape as desired. Asillustrated in FIG. 11C, the interfaces 127 and 129, in combination withthe base 124, define an isosceles triangle, though it should beappreciated that the interfaces 127, 129, and the base 124 couldalternatively define an equilateral triangle, a right triangle, anobtuse triangle, or any alternative geometric shape as desired.

Referring now to FIGS. 11A-C, each of the spikes 41A-C defines anabsolute height H_(A) with respect to the bone facing surface 26, and arelative height H_(R), when the endplate is horizontally oriented, withrespect to a common horizontal plane H extending along the lateral andlongitudinal directions, such as the inner transverse surface 45, or theinner transverse surface 43 of the upper endplate 20 when the implant 10is in a horizontally oriented, non-articulated, position. In accordancewith the illustrated embodiment, the absolute height H_(A) can bebetween 0.5 mm and 4.0 mm, including a range between approximately 1.5mm and approximately 2.5 mm, for instance a range between approximately1.5 mm and approximately 2.0 mm (see also FIG. 12B). The relative heightH_(R) can be between approximately 1.5 mm and approximately 10 mm,including a range between approximately 2.0 mm and approximately 7.0 mm.

In accordance with the illustrated embodiment, the relative height H_(R)of at least two of the spikes 41, up to all of the spikes 41, canincrease in a longitudinally rearward direction. Otherwise stated, thetransverse distance between a common horizontal plane from therespective outer transverse tip 126 of each spike 41 increases along thelongitudinally rearward direction. Accordingly, the relative height ofthe forward spike 41A is less than the relative height of the relativeheight of the middle spike 41B, which in turn is less than the relativeheight of the rear spike 41C. Because the portion 26 a of the bonefacing surface 26 that supports the spikes 41 is substantially planarand horizontal in accordance with the illustrated embodiment, therelationship of the absolute heights H_(A) of the spikes 41A-C withrespect to each other is as described with respect to the relativeheights H_(R) of the spikes 41A-C.

With continuing reference to FIGS. 11A-F, at least one, and up to all ofthe spikes 41A-C defines a recess 130 extending into at least one of thesurfaces 122 a-c. For instance, the forward spike 41A defines a recess130 extending into the laterally outer front surface 122 a and furtherdefines a recess 130 extending into the rear surface 122 c. The middlespike 41B defines a recess 130 extending into the laterally inner frontsurface 102 b. The rear spike 41C defines a recess 130 extending intothe laterally inner front surface 122 b and the rear surface 122 c. FIG.12B illustrates a recess 130 extending into the rear surface 122 c of aspike 41. FIGS. 12A and 12C illustrate a recess 130 extending into eachof the front surfaces 122 a and 122 b. FIG. 12D illustrates a recess 130extending into all surfaces 122 a-c. The recess 130 extending into thelaterally front surface 122 a extends between the front interface 125and the rear interface 127. Similarly, the recess 130 extending into thelaterally inner front surface 122 b extends between the front interface125 and the rear interface 129. The recess extending into the rearsurface 122 c extends between the rear interfaces 127 and 129.

Thus, in accordance with one embodiment, the recess 130 extends into therespective surface 122 along at least one or both of a lateraldirectional component and a longitudinal directional component.Furthermore, in accordance with one embodiment, the recess 130 projectsinward with respect to a plane defined by at least two outer edges ofthe surface 122 in which the recess 130 is disposed. Alternatively, theentire surface 122 can be provided in the shape of the recess 130.

Because at least one of the spikes 41 defines a recess 130 in its medialside, and at least one of the spikes 41 defines a recess 130 in itslateral side, movement of the implant 10 is restricted as the spikes 41penetrate the complementary vertebral surface 13 b. It should beappreciated, however, that the spikes 41A-C can alternatively define arecess in one or more, up to all, of the surfaces 122 a-c. For instance,the spikes 41 can define a first recess 130 in one of the surfaces 122,and a second recess 130 in another one of the surfaces 122.Alternatively or additionally, a single recess 130 can extend into apair of adjacent surfaces 122.

The recess 130 is vertically or transversely elongate, and extends upfrom the base 124 and terminates at a location transversely inward ofthe tip 126. In accordance with the illustrated embodiment, the recess130 is shaped as an arc in the horizontal plane, that is transverselyelongate so as to define a partial cylindrical surface, and can beprovided as a cut out of the corresponding surface or surfaces 122 a-c.For instance, a cylindrical bore 132 can be milled or otherwise formedinto the bone facing surface 26. The location of the bore 132 can bedisposed adjacent a desired surface of the spike 41, such that themilling operation cuts the cylindrically shaped recess 130 into thespike 41. It should be appreciated that the milling operation need notextend into the endplate 26, but could instead terminate once the recess130 has reached its desired transverse depth, for instance to the base124 of the spike 41. The depth of the recess 130 into the surface 122 ofthe spike 41 can thus depend on the alignment between the location ofthe bore 132 and the surface 122.

As illustrated in FIG. 11B, the recess 130 extending into the laterallyinner front surface 122 a of the rear spike 41C has a height greaterthan the recess 130 extending into the laterally inner front surface 122a of the middle spike 41B, though the height of the recess 110 of therear spike 41C could be equal to or less than that of the middle spike41C. Likewise, the height of the recess 130 extending into the outerfront surface 122 b of the forward spike 41A could be equal to, greaterthan, or less than, that of the recess 130 that extends into the innerfront surface 122 a of the middle spike 41B and rear spike 41C. Asillustrated in FIGS. 11D-F, the recesses 130 are arc-shaped intransverse cross section, and extend less than 180° as illustrated,though the arc can alternatively have any length as desired. Inaccordance with the illustrated embodiment, the arc length of therecesses 130 increases along an inner transverse direction. Of course,it should be appreciated that the arc length of the recesses 130 couldalternatively remain substantially constant along an inner transversedirection. Furthermore, it should be appreciated that the recesses 130can be provided as any shape projecting into the respective surface orsurfaces 122 of the spike 41, for instance a polygonal shape such astriangular, rectangular, oval or any other shape as desired. It has beenfound that the recesses 130 reduce the cross-sectional dimension of thespikes 41, and thus are easily penetrable into the complementaryvertebral surface 13 b.

It should be appreciated that while the spikes 41 have been described inaccordance with the illustrated embodiment, the spikes 41 can have anysuitable alternative shape as desired. For instance, one or more, up toall of the surfaces 122 a-c could be shaped in accordance with anysuitable alternative embodiment. It should further be appreciated thatthe spikes 41 are not intended to be limited to having the threesurfaces 122 a-c. Rather, in accordance with one embodiment, at leastone of the spikes 41 has at least one surface that defines a recess,such as the recess 120 as illustrated and described above.

It should be appreciated that while each group 120A-B includes threespikes 41 as illustrated, each group can include any number of spikes41, including less than three and more than three, for instance at leastone spike 41. It has been found that six spikes 41 projecting from thebone facing surface 26 provides adequate penetration into thecomplementary vertebral surface 13 b, while also providing adequatelyrobust fixation. The at least one spike 41 can be disposed at anylocation on the planar portion 26 a of the bone facing surface 26, orelsewhere on the bone facing surface 26.

Furthermore it should be appreciated that the lower endplate 22 includesat least one spike 41 that can be disposed at either the first lateralregion 51A, the second lateral region 51B, or coincident with thecentral longitudinal axis L-L. Furthermore, it should be appreciatedthat each of the spikes 41 can be constructed in accordance with any ofthe embodiments as described above with respect to spikes 41A-C. Itshould also be appreciated that the spikes 41A-C of the first group 120Acan be constructed substantially identically with respect to thecorresponding spikes 41A-C of the second group 120B as illustrated, oralternatively the spikes 41A-C of the first group 120A can beconstructed differently than the corresponding spikes 41A-C of thesecond group 120B.

The endplates 20 and 22 and various respective bone fixation spikes 39and 41 that project transversely out from the endplate 20 and 22 havebeen described in accordance with certain embodiments. However, asdescribed above, the endplates 20 and 22, along with the bone fixationspikes 39 and 41 can be constructed in accordance with numerousalternative embodiments. For instance, the spikes 39 and 41 can bearranged on their respective endplates as illustrated in FIG. 13A.Furthermore, at least one or more, up to all, of the spikes 39 and 41can be constructed in accordance with any of the embodiments illustratedbelow in FIGS. 13B-N, or alternatively can include at least one or moreup to all of the features or structures described below with respect tothe spikes illustrated in at least one or more up to all of FIGS. 13B-N.It should be appreciated that the various structure illustrated in FIGS.13B-N can be orientated in any direction as desired, such as alongitudinally forward direction, a longitudinally rearward direction, alaterally inward direction, a laterally outward direction, or anywherebetween these directions.

Referring now to FIG. 13A, an endplate 200 is illustrated, and can beconstructed as described with respect to endplates 20 or 22. Thus, theendplate 200 defines a longitudinally front end 202, an opposinglongitudinally rear end 204, and a pair of laterally opposing sides 206.A central longitudinal axis L-L divides the endplate 200 into opposinglateral sections 208 a and 208 b. The endplate 200 carries three groups210 a-c of bone fixation spikes 212. The groups 210 a-c of spikes 212can be arranged on the endplate 200 as described above with respect tothe groups 100A-B and 120A-B. However, FIG. 13A illustrates that morethan two groups of spikes 212 can be carried by an endplate, though itshould be appreciated that just one group can be carried by an endplate.In accordance with the illustrated embodiment, the first two groups 210a-b are disposed in the lateral sections 208 a-b, respectively, whilethe third group 210 c is arranged on the longitudinal axis L-L. Thus,the spikes 212 of one or more, up to all, of the groups can be inpartial or total longitudinal alignment. It should be appreciated thatFIG. 13A illustrates that the endplate 200 can carry more than sixspikes, and more than two groups of spikes. For instance, an endplatecan carry any number of laterally offset groups of spikes, for instanceone, two, three, four, five, or six groups or more. Each group caninclude at least one spike, including two, three, four, five, six,seven, eight, nine, ten, or more.

Referring now to FIGS. 13B-C, a bone fixation spike 220 is illustratedas including a base 222 and a tip 224 that is transversely spaced fromthe bone facing surface of the corresponding endplate in the mannerdescribed above. The bone fixation spike 220 includes four outersurfaces 226 a-d that extend between the base 222 and the tip 224, andare connected to each other at a 90° angle as illustrated. The outersurfaces 226 a-d all have the same horizontal length, such that thespike 220 is in the shape of a square in top plan view as illustrated inFIG. 13C, though the spike 220 could alternatively be rectangular, aparallelogram, quadrilateral, or other four-sided polygon as desired. Arecess 228 extends into at least one of the surfaces 226 a-d, andextends into all of the surfaces 226 a-d in the manner described abovewith respect to recesses 110 and 130. The recesses 228 can becylindrical, conical, triangular (having a pointed or rounded apex), orpolygonal, for instance including five polygonal surfaces of a pentagonas illustrated. Furthermore, the recesses 228 can be angulated withrespect to each other.

Referring now to FIG. 13D, a bone fixation spike 230 is illustrated asincluding a base 232 and a tip 234 that is transversely spaced from thebone facing surface 235 of a corresponding endplate in the mannerdescribed above. The bone fixation spike 230 includes a plurality ofouter surfaces, including outer surfaces 236 a-c that extend between thebase 232 and the tip 234. The outer surfaces 236 a and 236 c each joinopposing edges of the outer surface 236 b, so as to define respectiveinterfaces 238 a and 238 b. The interface 238 a extends from the base232 at an angle λ₁ which can be approximately 90°, while the interface238 b extends from the bone facing surface 235 at an angle λ₂ greaterthan 90°, such as between approximately 90° and 120°. The outer surfaces236 a and 236 c further define opposing edges 239 a and 239 b that areconnected between the base 232 and the tip 234 (e.g., extend from thebase 232 and the tip 234). Thus, the bone fixation spike 230 illustratesthat a bone fixation spike can include one or more edges that extendperpendicular to the base, or the underlying bone facing surface of thecorresponding endplate. The bone fixation spike 230 further illustratesthat one or more of the outer surfaces can be connected between the tipand the base, while one or more other outer surfaces can extend betweenthe tip and the base without being connected between the tip and thebase. A recess of the type described above can extend into one or more,up to all, of these outer surfaces.

Referring now to FIGS. 13E-F, a bone fixation spike 240 is illustratedas including a base 242 and a tip 244 that is transversely spaced fromthe bone facing surface of the corresponding endplate in the mannerdescribed above. The bone fixation spike 240 includes four outersurfaces 246 a-d that extend between the base 242 and the tip 244. Afirst pair of laterally opposing outer surfaces 246 a and 246 c aretriangular, while a second pair of longitudinally opposing outersurfaces 246 b and 246 d are rectangular. The rectangular outer surfaces246 b and 246 d converge toward each other in an outer transversedirection toward the tip 244, and are joined at the tip 244. Thus, thetip is elongate in a direction between the outer transverse apexes ofthe triangular outer surfaces 246 a and 246 c. The triangular surfaces246 a and 246 c can extend perpendicular from the underlying bone facingsurface. A recess 248 can extend into any or all of the surfaces 246a-d, and extends into the surfaces 246 b and 246 d as illustrated.

Referring now to FIG. 13G, a bone fixation spike 250 is illustrated asincluding a base 252 and a tip 254 that is transversely spaced from thebone facing surface of the corresponding endplate in the mannerdescribed above. The bone fixation spike 250 includes four outersurfaces 256 a-d that extend between the base 252 and the tip 254. Afirst pair of laterally opposing outer surfaces 256 a and 256 c aretriangular, while a second pair of longitudinally opposing outersurfaces 256 b and 256 d are quadrilaterals, shaped as trapezoids, andin particular isosceles trapezoids. The trapezoidal outer surfaces 256 band 256 d converge toward each other in an outer transverse directiontoward the tip 254, and are joined at the tip 254. The triangularsurfaces 256 a and 256 c also converge toward each other in an outertransverse direction, however the outer transverse ends of thetriangular surfaces 256 a and 256 c are spaced from each other, suchthat the tip 254 is elongate between the outer transverse ends. A recess258 can extend into any or all of the surfaces 256 a-d, and extends intothe surfaces 256 b and 256 d as illustrated.

Referring now to FIGS. 13H-I, a bone fixation spike 260 is illustratedas including a base 262 and a tip 264 that is transversely spaced fromthe bone facing surface of the corresponding endplate in the mannerdescribed above. The bone fixation spike 260 includes four outersurfaces 266 a-d that extend between the base 262 and the tip 264. Eachof the surfaces 266 a-d is triangular in shape, and in particulardefines an isosceles triangle. The triangular outer surfaces 266 a-dconverge toward each other in an outer transverse direction toward thetip 264, and are all joined at the tip 264. A recess 268 can extend intoany or all of the surfaces 266 a-d, and extends into all of the surfaces266 a-d as illustrated.

Referring now to FIG. 13J, a bone fixation spike 270 is illustrated asincluding a base 272 and a tip 274 that is transversely spaced from thebone facing surface of the corresponding endplate in the mannerdescribed above. As described above with respect to spike 39 and 41, itis recognized that spikes extending from an underlying bone facingsurface can include at least one outer surface. The bone fixation spike270 includes one outer surface 276 that has the shape of a cone. One ormore recesses 278, for instance between one and eight recesses 278, canextend into the outer surface 276 as desired, and can becircumferentially equidistantly or irregularly spaced about the outersurface 276. In accordance with the illustrated embodiment, the recesses278 can be 90° circumferentially offset about the conical outer surface276.

Referring now to FIG. 13K, a bone fixation spike 280 is illustrated asincluding a base 282 and a tip 284 that is transversely spaced from thebone facing surface of the corresponding endplate in the mannerdescribed above. The bone fixation spike 280 includes a plurality ofouter surfaces, such as outer surfaces 286 a-c that extend between thebase 262 and the tip 264. A single recess 288 can extend into all threesurfaces 286 a-c. It is thus appreciated that a single recess can extendinto two or more adjacent outer surfaces of a bone fixation spike.Furthermore, the recess 288 extends from the tip 284 to the base 282. Itshould be appreciated that the recess 288 is further disposed andextends between the tip 284 and the base 282.

Referring now to FIGS. 13H-I, a bone fixation spike 290 is illustratedas including a base 292 and a tip 294 that is transversely spaced fromthe bone facing surface of the corresponding endplate in the mannerdescribed above. The bone fixation spike 290 includes six outer surfaces296 a-f that define a hexagon. The outer surfaces 296 a-f converge alongan outer transverse direction, and join at the tip 294. A recess 298 canextend into one or more, up to all of the outer surfaces 296 a-f asillustrated.

Referring now to FIG. 14, during operation, the implant 10 is thenaligned with the intervertebral space 14. The vertebral bodies 12 a-bare retracted such that the anterior ends AE of the vertebral bodies areseparated generally along the caudal-cranial dimension a distancegreater than the posterior ends PE of the vertebral bodies 12 a-b areseparated. Thus, the intervertebral space 14 defines a caudal-cranialdimension at the anterior end AE that is greater than the caudal-cranialdimension of the intervertebral space 14 at the posterior end PE.Accordingly, the increase in height of the spikes 39 and 41 from theleading ends 23 and 47 toward the rear ends 25 and 31 of the endplates20 and 22, respectively, correspond generally to an increase in heightfrom the posterior end PE toward the anterior end AE of theintervertebral space 14.

It should be appreciated that the structure and features of the upperendplate 20 can be incorporated into the lower endplate 22, and thestructure and features of the lower endplate 22 can be incorporated intothe upper endplate 20. For instance, the shape of the bone facingsurface 26 of the lower endplate 22 can be constructed as described withrespect to the shape of the bone facing surface 24 of the upper endplate20. Furthermore, the upper endplate 20 can carry the inlay 48 in themanner described with respect to the lower endplate 22, and the lowerendplate 22 can carry the insert 44 in the manner described with respectto the upper endplate 20. Furthermore, one or more, up to all, of thespikes 39 of the upper endplate 20 can be constructed as described withrespect to one or more, up to all, of the spikes 41 of the lowerendplate 22. Likewise, one or more, up to all, of the spikes 41 of thelower endplate 22 can be constructed as described with respect to one ormore, up to all, of the spikes 39 of the upper endplate 20.

As the implant 10 is inserted into the intervertebral space 14, thespikes 39 and 41 initially slide freely into the intervertebral space14, and prior to full insertion begin to bite into the respectivevertebral surfaces 13 a-b. Thus, each spike 39 and 41 can leave a cutoutor track in the respective vertebral surfaces 13 a-b as the implant isincreasingly inserted into the intervertebral space 14. Because thespikes 39 and 41 are laterally offset from each other, the spikes 39 and41 do not ride in tracks created by forwardly disposed spikes and thusprovide improved primary fixation. Once the implant 10 has been fullyinserted into the intervertebral space 14, the retraction of thevertebral bodies 12 a-b is released, thereby causing the surfaces 13 a-bto return to their normal direction of extension, whereby the spikes 39and 41 project into the surfaces 13 a-b. The anterior spikes 39 and 41project deeper into the surfaces 13 a-b than the posterior spikes 39 and41.

It is to be appreciated that the orthopedic implant 10 can beconstructed as an intervertebral implant with any dimensions desirablefor implantation of any intervertebral space along the spine, includingbut not limited to the cervical and lumbar regions. Furthermore, whilethe implant 10 is configured as a total disc replacement device,implants constructed in accordance with the teachings described hereinare readily configurable for use with a range of bone-anchoredorthopedic prostheses. For instance, the implant 10 can be configured asa spinal fusion implant, an intervertebral cage, spacer, or corpectomydevice, long bone fixation plates and intramedulary nails and rods, bonefixation plates for fixation of craniomaxillofacial fractures,veterinary implants, and tips for guide wires.

The embodiments described in connection with the illustrated embodimentshave been presented by way of illustration, and the present invention istherefore not intended to be limited to the disclosed embodiments.Furthermore, the structure and features of each the embodimentsdescribed above can be applied to the other embodiments describedherein, unless otherwise indicated. Accordingly, those skilled in theart will realize that the invention is intended to encompass allmodifications and alternative arrangements included within the spiritand scope of the invention, for instance as set forth by the appendedclaims.

What is claimed is:
 1. An intervertebral implant, comprising: anendplate defining a rear end, a front end spaced forward from the rearend, and laterally opposed sides that extend between the front and rearends, the endplate defining an outer transverse bone facing surfaceconfigured to engage a respective adjacent vertebral surface, an innersurface opposite the outer transverse bone facing surface in atransverse direction, and a longitudinal axis that extends centrallybetween the laterally opposed sides from the rear end to the front end,wherein at least a portion of the endplate is made from a titanium; ajoint member configured to be carried by the endplate, the joint memberdefining a rounded surface that is configured to provide an articulatingjoint with a rounded surface of a complementary joint member carried bya second endplate so as to allow for universal movement between theendplate and the second endplate, wherein at least a portion of thejoint member is made from a cobalt chromium; a first bone fixation spikeand a second bone fixation spike that each extend from the outertransverse bone facing surface and are disposed on opposite sides of thelongitudinal axis, wherein 1) the endplate defines a recess that extendsfrom a first end having a first portion that extends into the first bonefixation spike in the transverse direction and a second portion thatextends into the outer transverse bone facing surface in the transversedirection, such that the recess terminates within the endplate at asecond end that is disposed between the inner surface and the outertransverse bone facing surface, and 2) the first bone fixation spike andthe outer transverse bone facing surface combine so as to define anenclosed perimeter of the first end of the recess.
 2. The intervertebralimplant as recited in claim 1, wherein i) the outer transverse bonefacing surface is substantially smooth, ii) the endplate defines asubstantially linear insertion direction into an intervertebral space,the insertion direction defined from the rear end toward the front endalong a direction parallel to the longitudinal axis, such that thelongitudinal axis defines substantially stationary orientation duringinsertion of the endplate into the intervertebral space; and iii) thefirst and second bone fixation spikes are spaced from each other alongthe substantially smooth outer transverse bone facing surface, each ofthe first and second bone fixation spikes projecting out from the outertransverse bone facing surface and having a base that is attached toouter transverse the bone facing surface, a substantially pointedoutermost tip that is outwardly spaced from the outer transverse bonefacing surface more than any other location of the bone fixation spike,and at least one outer surface that extends between the base and theoutermost tip, the base defining a forwardmost end that is spaced fromthe outermost tip in the insertion direction, wherein the first recessextends into the outer transverse bone facing surface at a locationbetween the outermost tip and the base, such that the at least one outersurface into which the recess extends faces at least partially forward,and the forwardmost end is spaced from the recess in the insertiondirection.
 3. The intervertebral implant as recited in claim 2, whereinat least one of the first and second bone fixation spikes defines atransverse axis extending between the outer transverse bone facingsurface and the outermost tip, and the recess extends inwardly into theat least one outer surface toward the transverse axis.
 4. Theintervertebral implant as recited in claim 2, wherein the outermost tipis spaced from the outer transverse bone facing surface along thetransverse direction that is perpendicular to the insertion direction,and the recess is arc shaped so as to define a partial cylindricalsurface along an entirety of the transverse direction along which therecess extends.
 5. The intervertebral implant as recited in claim 2,wherein the recess extends transversely from a location inwardly spacedfrom the outermost tip toward the base.
 6. The intervertebral implant asrecited in claim 2, wherein the first bone fixation spike issubstantially pyramidal and includes three surfaces extending betweenthe base and the outermost tip, and the recess extends into two of thethree surfaces.
 7. The intervertebral implant as recited in claim 2,wherein the recess of each does not extend into the forwardmost end,such that the first bone fixation spike is continuous from the outermosttip to the base along a direction that is at least partially defined bythe insertion direction.
 8. The intervertebral implant as recited inclaim 1, wherein the joint member is threadedly connected to theendplate.
 9. The implant as recited in claim 8, wherein the first andsecond bone fixation spikes are laterally staggered with respect to eachother.
 10. The implant as recited in claim 9, wherein the first andsecond bone fixation spikes are two of a plurality of bone fixationspikes, the plurality of bone fixation spikes comprises a longitudinallyforward spike, a longitudinally rear spike, and a middle spikepositioned longitudinally between the forward and rear spikes, whereinthe forward spike is disposed laterally inward with respect to themiddle and rear spikes, and the rear spike is disposed laterally betweenthe front and middle spikes.
 11. The implant as recited in claim 8,wherein the first and second bone fixation spikes are two of a pluralityof bone fixation spikes, and the plurality of bone fixation spikescomprises a first group of bone fixation spikes, and a second group ofbone fixation spikes constructed substantially identically with respectto the first group of bone fixation spikes, such that the second groupof bone fixation spikes is symmetrical with respect to the first groupof bone fixation spikes about the longitudinal axis.
 12. The implant asrecited in claim 11, wherein each of the plurality of bone fixationspikes projects out from the outer transverse bone facing surface andhas a respective base that is attached to the outer transverse bonefacing surface, a substantially pointed outermost tip that is outwardlyspaced from the bone facing surface more than any other location of thebone fixation spike, at least one outer surface that extends between thebase and the outermost tip, and a recess extending into at least one ofthe at least one outer surface at a location between the outermost tipand the base.
 13. The intervertebral implant as recited in claim 1,wherein the endplate further defines a pocket that extends into theinner surface, and the joint member is configured to be inserted intothe pocket such that the joint member is carried by the endplate. 14.The intervertebral implant as recited in claim 1, wherein the outertransverse bone facing surface defines a front section proximate thefront end, a rear section proximate the rear end, and an intermediatesection positioned forward of the rear end and rearward of the frontend, and the outer transverse bone facing surface defines a lengthmeasured from the rear end forward to the front end, such that a firstportion of the length measured from the rear end to the intermediatesection is different than a second portion of the length measured fromthe intermediate section to the front end.
 15. The intervertebralimplant as recited in claim 1, wherein the outer transverse bone facingsurface defines a front section proximate the front end, a rear sectionproximate the rear end, and an intermediate section positioned forwardof the rear end and rearward of the front end, and the outer transversebone facing surface is curved such that: 1) the outer transverse bonefacing surface tapers towards the inner surface as the outer transversebone facing surface extends away from the intermediate section andtowards one of the laterally opposed sides, and 2) the outer transversebone facing surface tapers towards the inner surface as the outertransverse bone facing surface extends away from the intermediatesection and towards the other of the laterally opposed sides.
 16. Theimplant as recited in claim 1, wherein, the endplate defines a heightmeasured between the outer transverse bone facing surface and the innersurface in the transverse direction, and the height at the front end isdifferent than the height at the rear end.
 17. An implant comprising: anupper endplate defining a first bone facing surface configured to engagean adjacent first vertebral surface, and an inner surface opposite thefirst bone facing surface in a transverse direction, the first bonefacing surface defining a rear section, and a front section spacedforward from the rear section in a longitudinal direction which isperpendicular to the transverse direction, the first bone facing surfacebeing curved such that: 1) the front section tapers toward the innersurface as the front section extends forward in the longitudinaldirection, and 2) the rear section flares away from the inner surface asthe rear section extends forward in the longitudinal direction, whereinat least a portion of the upper endplate is made from a titanium; afirst joint member configured to be carried by the upper endplate, thefirst joint member defining a rounded surface, wherein at least aportion of the first joint member is made from a cobalt chromium; and alower endplate defining a second bone facing surface configured toengage an adjacent second vertebral surface, wherein the second bonefacing surface is substantially planar and spaced from the first bonefacing surface along the transverse direction, and each of the endplatesdefines a rear end and a front end spaced forward from the rear endalong the longitudinal direction such that the front end is spaced fromthe rear end along a direction of insertion into an intervertebralspace, the upper and lower endplates each further defining respectivelaterally opposed sides extending between the respective front and rearends, the respective laterally opposed sides spaced from each otheralong a lateral direction that is perpendicular to both the longitudinaldirection and the transverse direction, wherein at least a portion ofthe lower endplate is made from a titanium; a second joint memberconfigured carried by the lower endplate, the second joint memberdefining a rounded surface that is configured to provide an articulatingjoint with the rounded surface of the first joint member so as to allowfor universal movement between the upper and lower endplates, wherein atleast a portion of the second joint member is made from a cobaltchromium; and a plurality of bone fixation spikes spaced along thelongitudinal direction, the bone fixation spikes projecting out from thefirst bone facing surface, wherein 1) each of the plurality of bonefixation spikes defines a footprint at the first bone facing surfacefrom a view in the transverse direction, 2) each of the plurality ofbone fixation spikes individually combines with the upper endplate todefine a respective single cylindrical recess, such that eachcylindrical recess is associated with only an individual one of theplurality of bone fixation spikes, each recess having a circularperimeter that is defined only by the respective individual one of theplurality of bone fixation spikes and the first bone facing surface, and3) the circular perimeter has a center that is positioned at the firstbone facing surface outside the footprint of the respective individualone of the plurality of bone fixation spikes.
 18. The implant as recitedin claim 17, wherein each of the plurality of bone fixation spikesdefines a base, an outermost tip that is outwardly spaced from the firstbone facing surface along the transverse direction, and a plurality ofside walls that extend out between the base and the outermost tip, eachof the plurality of bone fixation spikes defining a forwardmost end thatis attached to the first bone facing surface such that each of theplurality of bone fixation spikes slopes rearward as it extends from theforwardmost end to the outermost tip, wherein the outermost tip of eachof the plurality of bone fixation spikes has a transverse height withrespect to a common horizontal plane, and the transverse height of theoutermost tip of at least two of the plurality bone fixation spikesincreases along the longitudinal direction from the front end of thefirst bone facing toward the rear end of the first bone facing surface,wherein the recess extends into at least a select one of the side walls,the recess open in a direction, the direction defined by one or both ofthe lateral and the longitudinal directions, along an entirety of itslength from the base to a location disposed between the base and theoutermost tip.
 19. The implant as recited in claim 18, wherein therecess defines a length along a plane that is defined by thelongitudinal and lateral directions, and the length at a locationproximate to the outermost tip is less than the length at a locationproximate to the base.
 20. The implant as recited in claim 17, whereinthe rounded surface of the first joint member is concave, and therounded surface of the second joint member is convex.
 21. The implant asrecited in claim 20, wherein the first joint member is threadedlyattached to the upper endplate.
 22. The implant as recited in claim 20,wherein the lower endplate defines a pair of channels, and the secondjoint member includes a pair of guide wings that are insertable into thepair of channels, respectively, so as to attach the second joint memberto the lower endplate.
 23. The implant as recited in claim 17, whereinthe front section is proximate the front end, the rear section isproximate the rear end, and an intermediate section is positionedforward of the rear end rearward of the front end, the first bone facingsurface is curved such that the front section tapers toward the innersurface as the front section extends forward between the intermediatesection and the front end, and the rear section flares away from theinner surface as the rear section extends forward between the rearsection and the intermediate section.